The Pla surface protease/adhesin of Yersinia pestis mediates bacterial invasion into human endothelial cells

AbstractThe plasminogen activator Pla of Yersinia pestis belongs to the omptin family of enterobacterial surface proteases and is responsible for the highly efficient invasion of the plague bacterium from the subcutaneous infection site into the circulation. Y. pestis has been reported to invade human epithelial cells. Here, we investigated the role of Pla in bacterial invasion into human endothelial cells. Expression of Pla in recombinant Escherichia coli XL1(pMRK1) enhanced bacterial invasion into ECV304 cells. The invasiveness was not affected by substitution mutation at the residues S99 or D206 that are needed for the proteolytic activity of Pla. Pla-expressing bacteria adhered to the extracellular matrix of ECV304 cells. Only weak adhesion and poor invasion were seen with the recombinant E. coli XL1(pMRK2), which expresses the omptin homolog from E. coli. The results identify Pla as an invasion protein of Y. pestis and show that the invasive function does not involve the proteolytic activity of Pla

Systematic Review of Intelligent Tutoring Systems for Hard Skills Training in Virtual Reality Environments

Advances in immersive virtual reality (I-VR) technology have allowed for the development of I-VR learning environments (I-VRLEs) with increasing fidelity. When coupled with a sufficiently advanced computer tutor agent, such environments can facilitate asynchronous and self-regulated approaches to learning procedural skills in industrial settings. In this study, we performed a systematic review of published solutions involving the use of an intelligent tutoring system (ITS) to support hard skills training in an I-VRLE. For the seven solutions that qualified for the final analysis, we identified the learning context, the implemented system, as well as the perceptual, cognitive, and guidance features of the utilized tutoring agent. Generally, the I-VRLEs emulated realistic work environments or equipment. The solutions featured either embodied or embedded tutor agents. The agents’ perception was primarily based on either learner actions or learner progress. The agents’ guidance actions varied among the solutions, ranging from simple procedural hints to event interjections. Several agents were capable of answering certain specific questions. The cognition of the majority of agents represented variations on branched programming. A central limitation of all the solutions was that none of the reports detailed empirical studies conducted to compare the effectiveness of the developed training and tutoring solutions.Peer reviewe

Simulation of Crowd Egress with Environmental Stressors

This article presents a modeling framework to characterize evacuees' response to environmental stimuli during emergency egress, especially in fire and smoke condition. The model is developed in consistency with stress theory, which explains how an organism reacts to environmental stressors. We integrate the theory into the well-known social-force model and apply the method to simulate crowd evacuation behavior in building emergency egress. The algorithm has been tested in FDS+EVAC.Comment: 10 pages, 10 figure